We all know it by now: Sex isn't always as easy as rolling out of (or into) bed. In fact, in a survey of 32,000 women by researchers at Massachusetts General Hospital, 40% said they had a problem, whether it was low desire, dryness, or difficulty reaching orgasm. "Your sex life is bound to change as your body and your life change," says Bat Sheva Marcus, Ph.D., clinical director of the Medical Center for Female Sexuality in New York City. "That's normal." But don't assume that a slump means your sex life is over. Several recent studies have found that even many 80-year-olds are getting plenty of satisfaction (spelled o-r-g-a-s-m-s). The secret to lifelong passion? Finding ways to deal with common desire-killers. Here, a busy woman's guide to sizzling sex for life.

YOUR HORMONES ARE GOING HAYWIRE

When Jackie,* of Cortlandt Manor, NY, and her husband got married more than 20 years ago, they made a rule that they'd always have sex at least once a week unless one of them was sick. "We've pretty much stuck to it," she says. Still, several years ago, around the time Jackie turned 51, she realized their weekly rendezvous was more often than not a date with disappointment. "I was having problems with dryness, and I couldn't reach orgasm, even though I'd never had any difficulties before," she says. "I was worried I'd be dead below the waist for the rest of my life."

As estrogen drops in menopause, there's less blood flow to the vagina, a key component of arousal. Also, the tissue can become less moist, which makes it harder to get physically revved up and can make sex painful — sometimes excruciating. Similar problems often crop up after childbirth, especially if you're breast-feeding, because your estrogen is suppressed. Cancer treatments like chemotherapy, radiation, or surgery can cause difficulties, too. When Evelyn, 34, of Monroe, NY, went into early menopause after a hysterectomy due to uterine cancer, she started feeling "extremely dry down there" — and it had a dramatic impact on her desire. "My husband and I went from having sex three times a week to once a month," she says. "And when we did have sex, it was awful. It felt like my vagina was on fire."

If you're having pain during sex, or vaginal dryness, get an evaluation from a doctor, suggests Renee Horowitz, M.D., an ob/gyn and founder of the Center for Sexual Wellness in Detroit. "Hormonal changes can cause vaginal dryness, but so can a variety of other things — medications like antihistamines, antidepressants, and even the Pill, as well as certain skin conditions. Addressing underlying causes might take care of the problem."

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OTHER THINGS THAT CAN HELP:

OVER-THE-COUNTER LUBRICANTS
These are creams you apply to the vaginal area right before sex. Silicone- and oil-based products tend to work best, says Dr. Horowitz, because they don't dry out as quickly as water-based ones. (Steer clear of Vaseline and baby oil, though, because these can irritate the vulva and the vagina.)

MOISTURIZERS
Unlike in-the-moment lubricants, you use these every two or three days to provide ongoing moisturization. "If you're having a lot of problems with dryness, you can use both," says Dr. Horowitz. Different brands contain different ingredients--some have aloe and calendula; others, silicone or mineral oil — "so you may need to try several to find the one you like best," says Susan Kellogg, Ph.D., director of sexual medicine at the Pelvic & Sexual Health Institute of Philadelphia.

HORMONES
The vaginal canal is extremely sensitive to hormones. Using an estrogen cream, tablet, or ring inside the vagina restores some elasticity and increases moisture as well as the resilience of the tissue, explains James Simon, M.D., clinical professor of ob/gyn at George Washington University in Washington, DC, who has studied treatments for sexual problems. Directions vary by product, but typically you insert cream or tablets daily for two weeks, then one to three times a week for as long as you need to. With a ring, you insert it and leave it in place for three months, then replace it. You won't feel the ring during sex, says Dr. Horowitz, and men rarely do. All these products contain a very low dose of estrogen — much less than hormone-replacement pills or patches do — "so they're far safer," she says.

The hormone worked for Jackie. Her doctor prescribed an estrogen ring to treat the dryness, along with testosterone gel. Though known as the male hormone, testosterone fuels desire in both sexes, and, like estrogen, it declines with age. "I'm back to normal," says Jackie. "Better than normal. My orgasms are more intense now than they were in my 20s."

VAGINAL DILATORS
During menopause (or even a years-long dry spell without sex), the vaginal canal often shrinks and becomes less elastic. Having frequent sex during menopause stretches the tissue, which can help. But if you notice tightness or become sore, or if you have the sensation that your partner's penis is bumping up against something inside you, a doctor or physical therapist who treats sexual issues might prescribe a dilator, a smooth plastic device that you insert into the vagina for several minutes every day to gently stretch the tissue. If you're having a lot of pain, doctors typically recommend that you start with a small dilator and use it for just a minute or two per day, gradually working your way up to larger sizes and longer times. That approach helped Evelyn. "At first the dilator hurt so badly I had to grit my teeth, but by the 10th day, it was totally fine," she says. Her doctor also prescribed an estrogen cream. "Sex doesn't hurt at all now. Zero," she says. "It's such a relief."

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VIBRATORS
If you're having problems with arousal or orgasm, vibrators can help because they provide lots of stimulation. (Don't blush! In a 2009 survey of nearly 4,000 women, more than half said they'd used a vibrator — and those who had were less likely to have problems with sex.) "In a certain way, sex is a cost-benefit issue," says Marcus. "If it hurts or takes too much effort, you start to lose interest. Vibrators are great because they make it easier to have fun."

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YOUR LIFE IS...TOO MUCH

When Marina Kamen was 38, she was 100 pounds overweight, running her own record-producing company, and raising three kids. The only thing missing from her life: sex. "I felt like my body was completely unattractive. I didn't want to be naked in front of myself, much less my husband," she says. But it wasn't just the extra weight that was making her feel asexual: "I was consumed by all the stuff I was doing for everyone else and had lost a sense of my own fabulousness--and you need that to feel passion." Says Dr. Simon, "Sexuality is complex. It's not like a switch that you turn on or off. If you're stressed out at work or have little time for yourself or you're unhappy with your body — all those things can undermine your desire and your response to sex."

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Fatigue can cripple your libido, too — and even women who were once good sleepers may start tossing and turning in midlife, as hormonal changes cause night sweats and 3 A.M. awakenings. A 2009 National Sleep Foundation poll revealed that 19% of people who aren't getting enough sleep say they're too exhausted for sex, while in a 2012 survey from the Better Sleep Council, six in 10 people admitted craving sleep more than sex. "Sometimes I go to sleep thinking about sex, but I'm too tired to act on it," admits Dawniel Winningham, 41, of Houston. She launched a new company two years ago, but has kept her demanding day job as a bank vice president — and she has three teenagers. "Sex keeps getting pushed to the bottom of the list."

Emotional stress, the universal curse of multitasking women, doesn't help, either. Researchers at the University of Texas at Austin reported in 2010 that the stress hormone cortisol can block the effects of testosterone — so our overscheduled, pressure-cooker lives may be lowering our libido. But just as the demands of life can undermine your lust, these lifestyle changes can restore your connection with your sexy side:

EXERCISE
Not only does regular aerobic activity help you keep your weight under control and make you feel better about your body in general, but it also gives you increased energy and stamina and reduces stress — all important components of a robust sex drive. Studies have found that those who are more fit tend to feel sexier and have more sex. Exercise increases blood flow to the genitals, which can help with arousal, says Kellogg: "You don't have to be an elite athlete. Going for a brisk walk three to five times a week will help."

FIND WAYS TO DE-STRESS
Because cortisol physically undermines desire, it's critical to take concrete steps to calm down, whether it's by doing yoga, staying in touch with friends, or slipping into a warm bath before bed, says Dr. Horowitz.

SET THE MOOD
While losing weight helped Kamen feel better about her body, she's also learned that sex takes prepping. "I close the computer, turn off my cell phone, put on perfume and some nice, vibey music, and dim the lights," she says. "It helps to create a sexy atmosphere."

JUST DO IT
Even if you're not 100% in the mood. Research has shown that women's sexual response cycles are different from men's, and we may not experience a spontaneous, out-of-the-blue urge to merge. But if you can relax enough — and switch off the ticker tape of to-do's streaming through your mind — to start kissing and fondling your partner, you'll probably get turned on. "Women often think that if they don't feel as lustful as they did in their 20s, there's something wrong with them. But in fact the change from spontaneous sex drive to reactive is completely normal," says Dr. Simon. And good sex, he adds, will make you want more — the best possible upward spiral.

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YOU'RE CLASHING WITH YOUR MATE

Kerry, 42, of Oakland, CA, loves her husband, but she finds that the small daily annoyances in their relationship are a total turnoff. "I get resentful of the fact that he doesn't pick up his stuff around the house, and that he is less of a disciplinarian than I am with our kids," she says. "That resentment parlays into, 'You're bugging me. I don't want to have sex with you.' "

Long-term relationships aren't easy, and when something is wrong, sex is often one of the first things to suffer. In fact, tensions can set off a domino effect of negativity. "You're irritated with your partner, so you avoid sex, which creates stress in itself — and causes you to miss out on one of the most powerful ways couples bond and foster intimacy," says Dr. Simon. Just as sex makes you feel closer, lack of it can push you apart.

There's not a couple on earth who completely avoids relationship problems, but here are some ways to keep them out of the bedroom:

ADDRESS ISSUES, LARGE AND SMALL
A woman usually can't fall passionately into her husband's arms when she's fuming about the fact that he forgot to pay the mortgage or take out the trash. So, to defuse resentment, it's important to talk through issues before you're in bed. "If you're having trouble finding a solution, seek help from a good marriage therapist," advises Dr. Horowitz.

But don't wait for your relationship to be perfect before you consent to sex — it might take a long time (like forever). "You don't want to let every petty problem turn into a sexual impediment," says Kellogg.

SPICE THINGS UP
The brain chemical dopamine promotes sexual behavior — and it's stimulated by novelty. Long-term relationships tend to fall into familiar patterns, making it easy to get bored. "Whether it's where you do it, how you do it, when you do it, what you wear, what toys you use — change is really important," says Dr. Horowitz. "Sex is supposed to be fun, so it helps to approach it with an attitude of playfulness."

MAKE TIME TO RECONNECT
And put some effort into it. The novelty rule holds true outside the bedroom, too. "If you always go to the same Italian restaurant on Saturday night, try Thai or Vietnamese instead," says Kellogg. "Better yet, try white-water rafting or zip-lining, or take an improv class together. Sharing slightly scary experiences is a great way to bond." For Kerry, talking is the best aphrodisiac of all. "I need to share stuff with Matt and remind myself why I like him," she says. "When we take time to do that, I'm much more likely to say, 'Let's get naked' — and really enjoy the experience."